System and method for monitoring and controlling snubbing slips

ABSTRACT

A system and method for monitoring and controlling a snubbing unit having traveling slips and stationary slips are provided. Position sensors are associated with the slips for directly or indirectly detecting opened and closed positions of the slips, including detecting a rotational position of a crankshaft that drives the slips into engagement with a pipe. Load sensors are associated with the slips for detecting load status of the slips. A control system receives input signals from the sensors, and confirms that either the traveling slips or the stationary slips are loaded before releasing or allowing the release the opposing set of slips, when transferring the pipe string load from the one set of slips to the other set of slips.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/462,446 filed on May 2, 2012 entitled “System and Method forMonitoring and Controlling Snubbing Slips”, the contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a system and method for monitoring andcontrolling engagement and load transfer of load bearing components inwell intervention, completion, drilling, and workover equipment, andsnubbing units in particular.

BACKGROUND OF THE INVENTION

Well intervention, completion and drilling equipment are used to feedpipe into and out of subterranean wells. As an example, snubbing unitsare known in the oil and gas industry for facilitating access to a wellwhich is under pressure. A snubbing unit manipulates various tubularcomponents such as pipe, tubing, and bottomhole assemblies into and outof a well while controlling the well under pressure. A conventionalsnubbing unit includes stationary and traveling slips which are operatedsequentially to shift tubulars into and out of the well through awellhead, despite the possibility of heavy tubular loads which urge thetubulars to fall into the well (“pipe heavy”), or the reservoirpressure-generated forces on the tubulars, which urge the tubular out ofthe well (“pipe light”).

While snubbing into or out of the well, a transition or “balance point”occurs between pipe light and pipe heavy, where the pipe weight and thelift force exerted by the well acting on the cross-sectional area of thepipe string is substantially equal. Subsequently, hundreds of feet ofpipe can be moved with minimal effort.

Snubbing is conventionally controlled manually by an operator, whoactivates the traveling and stationary slips in sequence when snubbinginto or out of a well. The snubbing slips are load bearing componentsand rely on friction to restrain the tubulars or pipe string. However,it is not uncommon for an operator to release one set of load bearingcomponents accidentally, before transferring the load to the other setof load bearing components. Such an error may result in the pipe stringbeing dropped or ejected, placing personnel at risk and damagingequipment.

Therefore, there is a need in the art for a method and system whichmitigates the difficulties of the prior art.

SUMMARY OF THE INVENTION

The present invention is directed to a system and method for monitoringand controlling engagement and load transfer of load bearing componentsin well intervention, completion, drilling, and workover equipment.Without limitation, in one embodiment, the equipment comprises asnubbing unit.

In one aspect, the invention comprises a system for monitoring andcontrolling a snubbing unit for snubbing a pipe, the snubbing unithaving first and second slips operating in tandem to engage and move thepipe into or out of a well, the system comprising:

-   -   (a) a first actuation sensor associated with the first slip and        a second actuation sensor associated with the second slip,        wherein the actuation sensors directly or indirectly detect        engagement of the associated slip on the pipe; and    -   (b) a control system operatively connected to the first and        second actuation sensors and adapted to receive input signals        from the sensors, and configured to execute a method comprising        the step of confirming that either the first or second slip (the        “unloaded slip”) has engaged the pipe, before fully releasing,        or allowing the full release of the other one of the slips (the        “loaded slip”), when transferring the pipe string load from the        loaded slip to the unloaded slip.

In one embodiment, the first and second actuation sensors each comprisesa position sensor which determines the position of the slip, wherein theslip may move between first position engaging the pipe, and a secondposition disengaging the pipe. In another embodiment, the first andsecond actuation sensors each comprise a load sensor which determinesthe load status of the slip. If the slip is loaded, that indicates theslip has engaged the pipe. Conversely, if the slip is unloaded, the sliphas not engaged the pipe. Preferably, the system comprises both aposition sensor and a load sensor for each set of slips.

The control system is adapted to process the input signals to providemeasures of position and load status and comparing the measures topredetermined values, wherein the positions and load status of thetraveling slips or the stationary slips are confirmed if the measuresare equal to the predetermined values.

In one embodiment, the position sensor detects the position of a movingpart of a slip, or a position of a hydraulic cylinder rod which actuatesthe slip. In one embodiment, the position sensor comprises a flow meterwhich measures the flow of a hydraulic fluid used to energize ahydraulic cylinder. In one embodiment, the position sensor directly orindirectly detects a rotational position of a crankshaft that is drivenby the hydraulic cylinder rod and that drives the slip into engagementwith the pipe. The position sensor may comprise a cam rotated by thecrankshaft, a linear cam follower that translates rotational movement ofthe cam into linear movement, and a linear differential transformer formeasuring linear movement of the cam follower.

In one embodiment, the load sensor comprises an air bladder, a hydraulicbladder, an electronic load cell, a hydraulic load cell, or a straingauge. In one embodiment, the load sensor further comprises a pressuretransducer.

In another aspect, the invention comprises a method of running pipe witha snubbing unit for snubbing a pipe, the snubbing unit having first andsecond load bearing components, operating in tandem to move the pipeinto or out of a well, the method comprising the steps of:

-   -   (a) engaging the pipe with the first slip, and moving the second        slip to a first position;    -   (b) engaging the pipe with the second slip;    -   (c) confirming with a position sensor or a load sensor, or both        a position sensor and a load sensor, that the second slip has        adequately engaged the pipe before completely releasing the        first slip; and    -   (d) moving the second slip to a second position to move pipe        either into or out of the well.

In one embodiment, the step of confirming slip engagement with the pipecomprises a step of confirming that the slips have reached a closedposition, or determining whether or not the slips are bearing asubstantial load, or both.

In one embodiment of the method, at least step (d) is automated toprevent complete release of the first slips without confirmation thatthe second slips have adequately engaged the pipe. The term “automated”means that a system, without any operator intervention, prevents releaseof the stationary slips, without the necessary confirmation.

In one embodiment, the confirmation step comprises the step of measuringdirectly or indirectly measuring the rotational position of thecrankshaft that rotates the second slip into engagement with the pipe.

Additional aspects and advantages of the present invention will beapparent in view of the description, which follows. It should beunderstood, however, that the detailed description and the specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention as defined bythe appended claims, will become apparent to those skilled in the artfrom this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of an exemplary embodimentwith reference to the accompanying simplified, diagrammatic,not-to-scale drawings. In the drawings:

FIG. 1A is a schematic diagram showing an elevational view of a pipesnubbing unit. FIG. 1B is a schematic diagram of one embodiment of asystem of the present invention.

FIG. 2 is a schematic block diagram of the method of one embodiment ofthe present invention.

FIG. 3 is a schematic block diagram of the method of one embodiment ofthe present invention.

FIGS. 4 and 5 are a perspective view and a side view, respectively, ofone embodiment of a position sensor of the present invention thatmeasures the rotational position of a crankshaft driven by a hydrauliccylinder rod of a snubbing unit.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to a system and method for monitoringand controlling engagement and load transfer of load bearing componentsin well intervention, completion, drilling, and workover equipment. Whendescribing the present invention, all terms not defined herein havetheir common art-recognized meanings. To the extent that the followingdescription is of a specific embodiment or a particular use of theinvention, it is intended to be illustrative only, and not limiting ofthe claimed invention. The following description is intended to coverall alternatives, modifications and equivalents that are included in thespirit and scope of the invention, as defined in the appended claims.

One embodiment of the invention is described in the context of controlof hydraulic snubbing units. As used herein, the term “hydraulicsnubbing unit” means a hydraulically actuated unit including slips, ablowout preventer stack, and hydraulic jacks for inserting or pullingpipe strings, or tubing, and bottomhole assemblies from underbalanced orlive well conditions. In the hydraulic jacks, hydraulic pressures act oncylinders to produce a force which is transmitted to the pipe string sothat the snubbing unit performs the operation of pushing pipe into orpulling pipe from a well. Traveling slips transmit the lifting orsnubbing force from the hydraulic jack to the pipe string. However, itwill be understood by one skilled in the art that the method and systemdescribed herein may be applied to any well intervention, completion,drilling or workover equipment that utilizes load bearing componentsthat work in tandem to push pipe into or pull pipe from a wellbore,referred to herein as a “service unit”.

As used herein, the term “slip” means a load bearing component thatcomprises a gripping element (for example, a wedge-shaped piece of metalwith teeth) used to hold the pipe string in place. Typically, severalopposing sets of slips are included in a conventional snubbing unit,with particular slip sets being designated for “pipe heavy” and “pipelight” operations. Conventionally, the slips are “directional” in thatthey are configured to better resist movement of the pipe in onedirection. Stationary heavy slips may be mounted on the blowoutpreventer (BOP) stack and control the movement of heavy pipe. Travelingheavy slips are conventionally attached to the top of a jack plate andcontrol the movement of heavy pipe. Stationary snubbing slips areconventionally mounted on top of the BOP stack and hold tubing which isin a pipe light or neutral state. Traveling snubbing slips may bemounted in reverse orientation on a traveling jack plate and control themovement of the pipe string into or from the well. The travelingsnubbing slips typically hold tubing only when tubing is in the pipelight state.

The elements of the service unit or snubbing unit which are used toactuate the load bearing components, and other conventional elements ofsuch units, are not part of the claimed invention. For example,embodiments of the present invention may be implemented in service unitshaving rack and pinion actuation instead of hydraulic cylinder actuationof the traveling components. The operation of a conventional hydraulicsnubbing unit is commonly known to those skilled in the art and need notbe described in detail herein.

In one embodiment, a snubbing unit (10) comprises a bottom jack plate(12) and a top jack plate (14). The snubbing unit (10) has a stationaryheavy slip bowl (16), provided with an underlying blowout preventer(BOP) (18), a stationary snubbing slip bowl (20), and a number ofhydraulic cylinder jacks (22) for moving a traveling jack plate (24)vertically towards and away from the top jack plate (14). The hydrauliccylinder jacks (22) each comprise a hydraulic cylinder from whichextends a cylinder rod (26), the hydraulic cylinder being mountedbetween the bottom jack plate (12) and the top jack plate (14), and theuppermost end of the cylinder rod (26) being connected to a travelingjack plate (24). The traveling heavy slip bowl (28) and the travelingsnubbing slip bowl (30) are mounted to the traveling jack plate (24).The pipe (32) for snubbing passes through the traveling slip bowls (28,30), the stationary slip bowls (16, 20) and the BOP (18) as it continuesdownward into the wellbore (not shown).

The present invention relates to a system and method for monitoringengagement status of load bearing components in a service unit. In oneembodiment, the system and method further controls or directs actuationof the load bearing components to reduce the risk of dropping orejecting the pipe string. In general terms, the system and methodprovide confirmation to the control system and/or operator that slipshave closed and engaged the pipe, and thus have actually been loadedwith pipe. With this information, the control system and/or operatorwill then allow the opposing set of slips to fully release the load tothe loaded slips. In addition, the system and method may provideconfirmation that a set of slips have released its load.

In one embodiment, the invention comprises a system for monitoring andcontrolling a service unit having first and second load bearingcomponents operating in tandem to engage and move pipe into or out of awell, the system comprising:

-   -   (a) a first actuation sensor associated with the first load        bearing component and a second actuation sensor associated with        the second load bearing component, wherein the actuation sensors        directly or indirectly detect engagement of the load bearing        component on a pipe; and    -   (b) a control system operatively connected to the first and        second actuation sensors and adapted to receive input signals        from the sensors, and configured to execute a method comprising        the step of confirming that either the first or second load        bearing components have engaged the pipe, before fully        releasing, or allowing the full release of the opposing load        bearing component, when transferring the pipe string load from        one load bearing component to the other.

In one embodiment, the first and second slip actuation sensors eachcomprise a position sensor which determines the position of the slip. Inanother embodiment, the first and second slip actuation sensors eachcomprise a load sensor which determines the load status of the slip. Thepresence of load on the slip is indirect confirmation that the slip hasengaged the pipe. Preferably, the system comprises both a positionsensor and a load sensor for each set of slips.

In one embodiment, the position and load sensors detect position of theslips and load on the slips, respectively, and each generate signalsrepresentative of these parameters, and are operatively connected togauges or indicators which are visible to the service unit operator, andwhich may also be associated to visual, audible or tactile alarms whichalert the operator to condition that requires attention. In anotherembodiment, the position and load sensors transmit the signals to acontrol system (100). The control system comprises an interface (110), amemory (120), and a processor (130). The interface (110) may be aconventional interface that is used to receive and transmit data for acontroller, such as a micro-controller. The interface (110) isconfigured to receive signals from the position and load sensors.

The interface may be a conventional device for transmitting andreceiving data and may include multiple ports for transmitting andreceiving data. The ports may be conventional receptacles forcommunicating data via various means such as, a portable memory device,a PC or portable computer or a communications network. The interface(110) is coupled to the memory (120) and the processor (130).

The memory may be a conventional memory typically located within amicrocontroller that is constructed to store data and computer programs.The memory may store operating instructions to direct the operation ofthe processor when initiated thereby. The memory is a non-volatilememory and includes a threshold value section that is dedicated locationof the memory configured to store threshold values.

The processor may be a conventional processor such as a microprocessor.The processor includes a comparison component (132) that compares themeasured position and load sensor values to a threshold value. Asignaling or actuation component (134) is configured to allow or actuatefurther operation of particular slips, depending on the comparison step.If the measured values do not meet the predetermined values, then thecontrol system signals the operator accordingly, and may, in oneembodiment, automatically prevent further operation of the slips.

Thus, in one embodiment, operation of the slips (i.e., opening andclosing) is thus driven by pre-programmed thresholds of the respectivephysical quantities detected by the position sensors and load sensors.The control system may then signal the operator to actuate the slips, ormay directly control the slip actuators in an automated method. In asemi-automated process, the actuation of the slips may be initiated byan operator, but the actuation may be blocked by the control systemunless satisfactory position and load measurements are received by thesystem.

In one embodiment, load sensors (34A-D) are positioned so as to beassociated with each of the four sets of slips shown, for example, inFIG. 1. Suitable load sensors include, but are not limited to, an airbladder, a hydraulic bladder, an electronic load cell, a hydraulic loadcell, a strain gauge, or other appropriate weight sensor. The loadsensor may be incorporated assembled into the slips, or attached betweenthe slips and the load bearing structure member to which the slips aremounted. When loaded, the load sensor will provide a measurable value ofthe compressive or tensile load applied to the slip. The value will berelayed to the control system.

If the load sensor is a fluid-filled bladder, then a pressure transducerwithin the bladder may measure the pressure and send the information tothe control system.

Although the load on any given slip may exceed many tens of thousands ofpounds in a snubbing operation, the load sensors need not quantify theload above a threshold value which is a substantial load. For example,any load over 5,000 lbs is a substantial load, indicative of a positivegrip on the pipe by the slips. A substantial load may be any significantweight which is indicative of adequate slip engagement.

The position sensor may sense or detect the position of a slip eitherdirectly or indirectly. In one embodiment, the position sensor detectsthe physical position of a moving component of the slip, or a movingcomponent of the actuator which opens or closes a particular set ofslips, which may be a hydraulic cylinder and rod arrangement. Theposition of the moving component will be indicative of the position ofthe slip. Position sensors are well known in the art, and may includeelectronic proximity sensors, linear or rotary differentialtransformers, string potentiometers, or rotary or shaft encoders. In oneembodiment, the position sensor determines the position of the rod in anactuating hydraulic cylinder arrangement.

In one embodiment as shown in FIGS. 4 and 5, the slips of the snubbingunit (10) are actuated by a hydraulic cylinder and rod arrangement (40).The hydraulic cylinder (42) is pivotally attached to a connecting rod(44). One end of the connecting rod (44) is pivotally connected to afirst crank shaft (46), which is turn connected to a first half (48) ofthe slip. The opposite end of the connecting rod (44) is pivotallyconnected to a second crank shaft (50), which is in turn connected to asecond half (52) of the slip. The connecting rod (44) translateshorizontal movement of the hydraulic cylinder rod (42) into rotationalmoment of the crank shafts (46, 50), which rotate the halves (48, 52) ofthe slip into engagement with a pipe (not shown). A cam (54) attached tothe first crankshaft (46) translates rotational movement of the firstcrankshaft (46) into linear movement of a cam follower (56) that isbiased by a spring against the cam (54). A linear differentialtransformer (58) measures the movement of the cam follower (56) andtransmits data indicative of this position to the processor. Based onthe geometric relationships between the foregoing parts, the processorof the system correlates the position of the cam follower (56) to theposition of either the half (48) of the slip or of the hydrauliccylinder rod (42), to confirm whether the first half (48) of the sliphas engaged the pipe. In one embedment, the engagement of the secondhalf (52) of the slip with the pipe can be confirmed in the same manner.

In another embodiment, the position sensor may comprise a flow meterwhich measures the volume of hydraulic oil which was used to eitherextend or retract the hydraulic cylinder rods from or into theircorresponding hydraulic cylinders. The volume required to open the slipsis calibrated by opening the slips from the closed position. The volumeis recorded for use in confirming that the slips have fully opened. Thevolume required to close the slips is calibrated by closing the slipsfrom the open position and recorded for use in confirming that the slipshave fully closed.

The volume required versus the position of the cylinder rod is adirectly linear relationship. A volume measurement may thus be used toindirectly determine the position of the slips during closing andopening. For example, if the volume used to close the slips was 75% ofthe calibrated volume, then it may be inferred that the slip hydrauliccylinder rod moved only 75% of the distance required to fully close theslips on the pipe string. Such information provides the control systemand/or operator with confirmation that the slips did not completelyclose as required.

In one embodiment, the system may further comprise a measurement systemfor measuring the movement of the hydraulic valves which fill or emptythe hydraulic cylinders which actuate the slips. The hydraulic valvesmove into either an open position to allow the flow of pressurizedhydraulic oil, or a closed position to prevent the flow of the hydraulicoil. The hydraulic oil in turn powers the hydraulic cylinders to openand close the slips. By measuring the opening or closing of thehydraulic valves, the control system may determine if the hydraulicvalves have successfully completed the desired action, and are properlyfunctioning.

In operation, the system monitors the slip position and load sensors todetermine if a specific slip actuation has been completed successfully.If the sensors indicate that the required actions have been completed,the control system will emit a signal to operate, or allow operation ofthe opposing set of slips to which the load is being transferred. If theposition sensors and/or load sensors do not generate successful (i.e.,pipe engagement) signals, then the control system will not release theopposing set of slips, or the operator is warned not to release theopposing set of slips.

The control system will provide the operator with confirmation that theload has been transferred to the slips which have been actuated. Theoperator will thus be aware that the slips have a sufficient hold on thepipe string, so as to be confident in releasing the opposing slips. Theload and position sensors may also provide confirmation that previouslyloaded slips have released its hold on the pipe string, and thus hasbeen relieved of its load.

The control system may have features for recording events or maintenanceincluding, but not limited to, event logging with real time clock fordata time stamping, and logging of system configuration changes to trackthe system configuration history and the identity of the operatorperforming the configuration changes. Display means which are eitherconnected to or integral with the control system display indicationsignals (for example, system status, errors, alarms, output messages,instructions, audible buzzers) to inform an operator whether aparticular slip is opened or closed.

The following is a specific example of one embodiment of the presentinvention. This example demonstrates how the system of the presentinvention can be used for monitoring and controlling slips of a snubbingunit to reduce the risk of dropping or ejecting the pipe string. Thisexample is offered by way of illustration and is not intended to limitthe claimed invention in any manner.

A method of the present invention may be implemented in the operation ofany service unit, where load bearing components operating in asequential manner for running pipe into or out of a well, comprising thesteps of:

-   -   (a) engaging the pipe with a first load bearing component and        moving a second load bearing component to a first position;    -   (b) engaging the pipe with the second load bearing component;    -   (c) confirming with a position sensor or a load sensor, or both        a position sensor and a load sensor, that the second load        bearing component has adequately engaged the pipe before        completely releasing the first load bearing component; and    -   (d) moving the second load bearing component to a second        position to move pipe either into or out of a wellbore.

Exemplary steps are presented schematically in FIG. 2 for removing pipestring from the well, in a pipe heavy situation, by transferring theload from the stationary heavy slip to the traveling heavy slip. Thismay be achieved by the operator closing the traveling heavy slips on thepipe string by actuating the slip hydraulic cylinders. As the hydrauliccylinders move the cylinder rods downwardly, the positioning sensordetects and senses the movement, generates a signal representative ofthe position of the cylinder rod, and transmits the signal to thecontrol system.

If the traveling heavy slips have not yet completely closed, the controlsystem may provide a signal (for example, audible, visual or electronic)to the operator notifying of the incomplete action, and the paired slipsmay be disabled. If the traveling heavy slips have completely closed,the control system interprets the signal as a completed, successfulaction, and the paired slips may be enabled or actuated.

With the traveling heavy slips fully closed to restrain the pipe string,the operator may then begin to transfer the pipe string load from thestationary heavy slips to the traveling heavy slips, by moving thetraveling heavy slips slightly upward. The load sensors associated withthe traveling heavy slips will sense and detect the load, generate asignal representative of the load, and transmit the signal to thecontrol system for processing and analysis. In one embodiment, if theload reaches a minimum threshold level, for example 5,000 pounds, thecontrol system will interpret the signal as a completed, successfulaction. Before the load reaches the minimum threshold level, the controlsystem will provide a signal to the operator, and may block release ofthe stationary slips.

If the traveling heavy slips are not loaded, the control system emits asignal to the operator notifying of the incomplete action, and mayautomatically prevent the stationary heavy slips from disengaging. Ifthe traveling heavy slips are loaded, the control system interprets thesignal as a completed, successful action.

If the signals from either or both of the positioning sensors and loadsensors are not indicative of successful travelling slip engagement withthe pipe, the control system will signal the operator accordingly, andmay not permit disengagement of the stationary slips. Once the travelingheavy slips are both properly loaded and restraining the pipe string,the control system then signals the operator and permits actuation ofthe stationary heavy slips which can be released from the pipe string toallow its removal from the well.

Exemplary steps are presented schematically in FIG. 3 for inserting thepipe string into the well, in a pipe light configuration, bytransferring the load from the traveling snubbing slip to the stationarysnubbing slip. Once the traveling snubbing slip has reached the bottomof its stroke, the operator then closes the stationary snubbing slips onthe pipe string by actuating the hydraulic cylinders. As the hydrauliccylinders move the cylinder rods, the positioning sensor detects andsenses the movement, generates a signal representative of the positionof the cylinder rod, and transmits the signal to the control system forprocessing and analysis.

If the stationary snubbing slips have not completely closed, the controlsystem emits a signal to the operator notifying of the incompleteaction, and may automatically prevent the traveling snubbing slips fromactuating. If the stationary snubbing slips have completely closed, thecontrol system interprets the signal as a completed action.

With the stationary snubbing slips fully closed to restrain the pipestring, the operator may then begin to transfer the pipe string loadfrom the traveling snubbing slips to the stationary snubbing slips, bymoving the traveling snubbing slips slightly upward. The load sensorssense and detect the resulting load on the stationary snubbing slips,generate a signal representative of the load, and transmit the signal tothe control system.

If the stationary snubbing slips are not sufficiently loaded, thecontrol system emits a signal to the operator notifying of theincomplete action, and may automatically prevent the traveling snubbingslips from disengaging. If the stationary snubbing slips are loaded, thecontrol system interprets the signal as a completed action.

If the signals from either or both of the positioning sensors and loadsensors are not indicative of successful stationary slip engagement withthe pipe, the control system will signal the operator accordingly, andmay not permit disengagement of the travelling snubbing slips. Once thestationary snubbing slips are both properly loaded and restraining thepipe string, the control system then emits a signal to actuate thetraveling snubbing slips which can be released from the pipe string toallow the hydraulic cylinders to jack up the traveling snubbing slips.The sensors and method of transferring the pipe from the stationarysnubbing slips to the traveling snubbing slips is initiated andcompleted to allow the traveling snubbing slips to insert the pipestring into the well.

The functionality and features associated with the control system asdescribed above and in accordance with the embodiments may beimplemented in the form of one or more software objects, components, orcomputer programs or program modules in the server and/or the clientmachines. The control system and methods described above may beimplemented in software, firmware or hardware, or combinations thereof.The system components shown in the Figures or described above may be ormay include a computer or multiple computers. The components may bedescribed in the general context of computer-executable instructions,such as program modules, being executed by a computer. Generally,program modules include routines, programs, objects, components, datastructures, etc., that perform particular tasks or implement particularabstract data types. Further, at least some or all of the softwareobjects, components or modules can be hard-coded into processing units,programmable devices, and/or read only memories or other non-volatilestorage media. The specific implementation details of the softwareobjects and/or program modules will be within the knowledge andunderstanding of one skilled in the art.

Thus, the control system may comprise a processing unit which operatesunder stored program control, for example, software or firmware storedin memory or other non-volatile storage media, may utilize any of a widevariety of other technologies including a special purpose computer, amicrocomputer, mini-computer, mainframe computer, programmedmicroprocessor, micro-controller, peripheral integrated circuit element,a CSIC (Customer Specific Integrated Circuit), ASIC (ApplicationSpecific Integrated Circuit), a logic circuit, a digital signalprocessor, a programmable logic device such as an FPGA (FieldProgrammable Gate Array), PLD (Programmable Logic Device), PLA(Programmable Logic Array), RFID processor, smart chip, or any otherdevice or arrangement of devices that is capable of implementing thesteps of the processes of the invention.

The computer system may include a general purpose computing device inthe form of a computer including a processing unit, a system memory, anda system bus that couples various system components including the systemmemory to the processing unit. Although many internal components of thecomputer or microprocessor device are not shown or described, those ofordinary skill in the art will appreciate that such components and theinterconnections are well known.

As will be apparent to those skilled in the art, various modifications,adaptations and variations of the foregoing specific disclosure can bemade without departing from the scope of the invention claimed herein.

What is claimed is:
 1. A system for monitoring and controlling asnubbing unit for snubbing a pipe, the snubbing unit having first andsecond slips operating in tandem to engage and move the pipe into or outof a well, the system comprising: (a) a first actuation sensorassociated with the first slip and a second actuation sensor associatedwith the second slip, wherein the actuation sensors directly orindirectly detect engagement of the associated slip on the pipe; and (b)a control system operatively connected to the first and second actuationsensors and adapted to receive input signals from the sensors, andconfigured to execute a method comprising the step of confirming thateither the first or second s slip (the “unloaded slip”) has engaged thepipe, before fully releasing, or allowing the full release of the otherone of the slips (the “loaded slip”), when transferring the pipe loadfrom the loaded slip to the unloaded slip.
 2. The system of claim 1wherein the method comprises the further step of confirming that theloaded slip has fully released the pipe and has become unloaded.
 3. Thesystem of claim 1, wherein an actuation sensor comprises a positionsensor for detecting a position of the associated slip.
 4. The system ofclaim 1, wherein the position sensor comprises a flow meter formeasuring a volume of hydraulic fluid flowing into or out of a hydrauliccylinder which actuates the associated slip.
 5. The system of claim 1wherein the position sensor directly or indirectly detects the positionof a moving part of the associated slip or a moving part of a componentwhich actuates the associated slip, which is indicative of the positionof the associated slip.
 6. The system of claim 5 wherein the positionsensor directly or indirectly detects the position of a hydrauliccylinder rod which actuates a slip of the associated slip.
 7. The systemof claim 6 wherein the position sensor directly or indirectly detects arotational position of a crankshaft that is driven by the hydrauliccylinder rod and that drives the slip into engagement with the pipe. 8.The system of claim 7 wherein the position sensor comprises a camrotated by the crankshaft, a linear cam follower that translatesrotational movement of the cam into linear movement, and a lineardifferential transformer for measuring linear movement of the camfollower.
 9. The system of claim 1, wherein any one of the actuationsensors comprises a load sensor for detecting a load on the associatedslip.
 10. The system of claim 9, wherein the load sensor comprises anair bladder, a hydraulic bladder, an electronic load cell, a hydraulicload cell, or a strain gauge.
 11. The system of claim 10, wherein theload sensor comprises a pressure transducer.
 12. The system of claim 1wherein any one of the actuation sensors comprises both a positionsensor for detecting a position of the associated slip and a load sensorfor detecting a load on the associated slip.
 13. The system of claim 1wherein the control system further comprises a component which permitsor blocks actuation of one of the slips depending on the status of theother slip.
 14. A method of running a pipe into or out of a well with asnubbing unit for snubbing a pipe, the snubbing unit having a first slipand a second slip operating in a sequential manner to engage and movethe pipe into or out of the well, the method comprising the steps of:(a) engaging the pipe with the first slip and moving the second slip toa first position; (b) engaging the pipe with the second slip; (c)confirming with a position sensor or a load sensor, or both a positionsensor and a load sensor, that the second slip has adequately engagedthe pipe before completely releasing the first slip; and (d) moving thesecond slip to a second position to move pipe either into or out of thewell.
 15. The method of claim 14 wherein the confirmation step comprisesthe step of determining whether or not the second slip has reached aclosed position engaging the pipe, or determining whether or not thesecond slip is bearing a substantial load, or both.
 16. The method ofclaim 15 wherein a control system prevents complete release of the firstslip unless it is confirmed that the slip has adequately engaged thepipe.
 17. The method of claim 14 wherein the confirmation step comprisesthe step of directly or indirectly measuring the rotational position ofthe crankshaft that drives the second slip into engagement with thepipe.